The present invention relates to a new and improved construction of an arrangement or apparatus for controlling the pressing force at the contact zone between a roll and one or a number of counter elements, the roll being constituted by a controlled deflection roll, the bending-through or sag of which can be adjusted by means of force-applying sources which are distributively arranged in the direction of the lengthwise axis of the controlled deflection roll and bear against a common roll support or beam.
Such type of rolling apparatuses have, for instance, multifarious fields of application in the fabrication of paper, in metal rolling mills and so forth. Sometimes there are provided, apart from the aforementioned force-applying sources, also counter force-applying sources which impart to the roll shell of the controlled deflection roll, in conjunction with the force-applying sources, a bending line which is more favourable for the intended fields of application. The principle of one such type of rolling apparatus has been described and illustrated in German Patent Publication No. 2,325,721, published Apr. 29, 1976 in different constructional embodiments. In such patent there is also disclosed that the force-applying sources, if desired combined into groups, can be individually controlled. One such group can be constituted by a single force-applying source, or however more than ten force-applying sources.
As the force-applying source there can be used not only the hydrostatic support bearings or support elements as disclosed in the aforementioned German Patent Publication No. 2,325,721, but also, for instance, electromagnetic arrangements.
A roll arrangement containing such electromagnetic force-applying sources has been disclosed in German Patent Publication No. 2,658,854, and the cognate U.S. Pat. No. 4,062,097, granted Dec. 13, 1977. This prior art arrangement encompasses a common adjustment element, by means of which it is possible to determine once and for all the magnetization current for all force-applying sources. Arranged after such adjustment element are the so-called "regulators", by means of which there can be individually readjusted or regulated the magnetization current of the individual force-applying sources. However, the construction of the last-mentioned components has not been disclosed.
Within the ambit of the present invention it is intended to also designate such components as "controllable force-applying sources" which load relieve at discrete locations a roll shell sector throughout its entire length or portions thereof and which roll shell sector is under load or force, in other words actual "force sinks" or also devices of the type disclosed in German Patent Publication No. 2,332,861 and the cognate U.S. Pat. No. 3,879,827, granted Apr. 29, 1975.
The control of the individual force-applying sources or groups of force-applying sources (herein sometimes referred to as "groups") is problematic. More specifically, the following conditions should be taken into account:
First of all, the force-applying sources must compensate the inherent weight of the roll shell. The influence of this magnitude or parameter can vary as a function of the spacing of the group from the ends of the roll shell, dependent upon the manner in which the roll shell is additionally mounted, at its ends or also near to the roll center.
Furthermore, the force-applying sources also must take-up the inherent weight of the counter element, for instance the roll or band, which is possibly arranged above the controlled deflection roll. Frequently, they often must, in fact, take-up the inherent weight of still further rolls of a calender arrangement, and depending upon the spacing from the roll ends different gravitational effects may be present, and also there must be taken into account possible arching or doming of the counter element.
What however should actually be controlled is the pressing force, for instance the "mean pressing force" as the actual magnitude or parameter which is decisive for the field of application. Additionally, there should be further taken into account that, for instance, during the pressing operation there is not only to be undertaken a uniform web processing, for instance thickness reduction of the material over the web width, in other words there should be accomplished at the same time throughout the length of the roll not only a uniform web processing, but quite frequently there must be imparted uniformity to possibly present irregularities in the web material which are caused by the processing of the web material at upstream located equipment or machinery. This means that the machine operator should be capable of individually controlling the force-applying sources or groups. Under the expression "mean pressing force" or "mean line force" there is to be understood the value of this force which is meaned or averaged over the length of the pressing gap or nip.
It is known to simulate the mechanical construction of a roll system by means of a model and to tap-off thereat control signals, by means of which it is possible to act upon the force-applying sources of the roll system itself. In this respect attention is directed to German Patent Publication No. 2,825,706 and the cognate U.S. Pat. No. 4,222,324, granted Sept. 16, 1980. This control arrangement is relatively complicated, and there is needed a separate model for each individual field of application.